1. Field of the Invention
This invention relates to an electrophotographic cleaning blade (cleaning blade for electrophotography) for removing toner remaining on an image bearing member (photosensitive drum), a transfer belt, an intermediate transfer member and so forth, used in an electrophotographic apparatus, and relates to an electrophotographic apparatus to which the cleaning blade is applied.
2. Description of the Related Art
The electrophotographic apparatus is provided with various cleaning blades for removing toner remaining on an image bearing member (photosensitive drum), a transfer belt, an intermediate transfer member and so forth. The blades of such cleaning blades are produced using a thermoplastic or thermosetting polyurethane resin or the like. From the viewpoint of plastic deformation and wear resistance, they are produced chiefly using a thermosetting polyurethane resin.
However, where a conventional blade made of a polyurethane resin is used, the coefficient of friction between polyurethane resin and the photosensitive drum is so large that the blade may turn up or the driving torque of the photosensitive drum is required to be made large. It may also come about that the leading edge of the blade is entwined by the photosensitive drum or the like and is stretched and cut to chip away. Such problems remarkably arise especially when the blade has low hardness, so that it may become insufficient in durability. On the other hand, when the blade has high hardness, it may scratch the photosensitive drum during operation.
To resolve such problems the blade made of a polyurethane resin has, a cleaning blade and a production process thereof are proposed where the cleaning blade is provided with a cured layer of 0.12 to 1.2 mm in thickness where the blade comes into contact with the photosensitive drum (e.g., Japanese Patent Laid-open Application No. 2001-343874). The cured layer is provided by allowing the polyurethane resin that is the base material of the blade to react with an isocyanate compound.
Further analyses made in detail in respect of the blade turning-up and chipping of the cleaning blade have revealed that the blade tends to turn up more at both end portions in its lengthwise direction. The reason therefor is that both end portions of a photosensitive drum correspond positionally to blank areas on both sides of a recording sheet and hence no image is formed there. Thus, in the areas where no image is formed, the amount of toner remaining on the photosensitive drum surface comes to be extremely small, and hence the slipperiness of the blade locally deteriorates only in such areas and the turning-up is liable to occur at both end portions.
It is effective in inhibiting the turning-up that, as in the past, the hardness of the blade is increased in the whole region of the part coming into contact with the photosensitive drum. However, there is a risk that blades whose contact portions are rough are produced in the production process. When taking a countermeasure against that, the process of removing the isocyanate compound inevitably increases, and a rise in material costs is brought about by increasing the hardness of the whole region of the part coming into contact with the photosensitive drum (e.g., Japanese Patent Laid-open Application No. 2004-280086).
On the contrary, even if the blade becomes rough to a certain extent at contact portions, there is no possibility of causing a problem as long as the touch portions fall within the end regions where no image is formed, i.e., regions other than what is called an image formation region. Accordingly, the cured layer is formed only at both end portions of the blade, so that it is considered that the step of removing an excess isocyanate compound can be simplified and material costs can be reduced, achieving good productivity and enabling the blade to be effectively prevented from turning up.
Hitherto, a method has been proposed in which the cured layer is provided only at both end portions of the blade (e.g., Japanese Patent Laid-open Application No. 2003-122222). However, Japanese Patent Laid-open Application No. 2003-122222 does not specify the hardness of the cured layer. There are risks that the blade turns up if the hardness is low and the photosensitive drum is scratched if the hardness is too high.